From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from tx2outboundpool.messaging.microsoft.com (tx2ehsobe004.messaging.microsoft.com [65.55.88.14]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "MSIT Machine Auth CA 2" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 7FAA72C00A8 for ; Wed, 29 May 2013 02:33:09 +1000 (EST) Date: Tue, 28 May 2013 11:32:53 -0500 From: Scott Wood Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling To: David Gibson In-Reply-To: <20130525024524.GA6112@boomeroo.fritz.box> (from david@gibson.dropbear.id.au on Fri May 24 21:45:24 2013) Message-ID: <1369758773.18630.1@snotra> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; delsp=Yes; format=Flowed Cc: kvm@vger.kernel.org, Alexey Kardashevskiy , linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, Alexander Graf , Paul Mackerras , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 05/24/2013 09:45:24 PM, David Gibson wrote: > On Wed, May 22, 2013 at 04:06:57PM -0500, Scott Wood wrote: > > On 05/20/2013 10:06:46 PM, Alexey Kardashevskiy wrote: > > >diff --git a/arch/powerpc/kvm/powerpc.c =20 > b/arch/powerpc/kvm/powerpc.c > > >index 8465c2a..da6bf61 100644 > > >--- a/arch/powerpc/kvm/powerpc.c > > >@@ -396,6 +396,7 @@ int kvm_dev_ioctl_check_extension(long ext) > > >+++ b/arch/powerpc/kvm/powerpc.c > > > break; > > > #endif > > > case KVM_CAP_SPAPR_MULTITCE: > > >+ case KVM_CAP_SPAPR_TCE_IOMMU: > > > r =3D 1; > > > break; > > > default: > > > > Don't advertise SPAPR capabilities if it's not book3s -- and > > probably there's some additional limitation that would be > > appropriate. >=20 > So, in the case of MULTITCE, that's not quite right. PR KVM can > emulate a PAPR system on a BookE machine, and there's no reason not to > allow TCE acceleration as well. That might (or might not; consider things like Altivec versus SPE =20 opcode conflict, whether unimplemented SPRs trap, behavior of =20 unprivileged SPRs/instructions, etc) be true in theory, but it's not =20 currently a supported configuration. BookE KVM does not support =20 emulating a different CPU than the host. In the unlikely case that =20 ever changes to the point of allowing PAPR guests on a BookE host, then =20 we can revisit how to properly determine whether the capability is =20 supported, but for now the capability will never be valid in the =20 CONFIG_BOOKE case (though I'd rather see it depend on an appropriate =20 book3s symbol than depend on !BOOKE). Or we could just leave it as is, and let it indicate whether the host =20 kernel supports the feature in general, with the user needing to =20 understand when it's applicable... I'm a bit confused by the =20 documentation, however -- the MULTITCE capability was documented in the =20 "capabilities that can be enabled" section, but I don't see where it =20 can be enabled. -Scott=